Technical Field
The present invention relates to a recording device discharge position adjustor and an image forming apparatus incorporating the adjustor.
Background Art
Image forming apparatuses employing an inkjet method are known, in which a plurality of recording devices discharges liquid droplets of a plurality of colors, respectively, onto a recording medium, such as a sheet of paper, and the discharged colors are superimposed on the recording medium, thereby forming a full-color image on the recording medium.
The image forming apparatus as described above includes a first head unit as a recording device to discharge liquid droplets of an ink liquid onto the sheet and a second head unit disposed downstream of the first head unit in a sheet conveyance direction, with both head units disposed along the sheet conveyance direction. A head unit displacer can move the second head unit laterally in a direction perpendicular to the sheet conveyance direction. Edge sensors to detect the lateral edge of the sheet are disposed upstream of the first head unit and the second head unit. When the sheet skews while being conveyed, the second head unit is displaced laterally by a displacement amount based on an output from each edge sensor, so that a relative positional error of the discharge position of the second head unit to the sheet relative to the discharge position of the first head unit to the sheet is corrected.
However, because the edge sensors are disposed upstream of each head unit in the sheet conveyance direction, they cannot directly detect an edge position of the sheet at a position of the head unit. Due to a change of the edge position sideways caused by skew/wobbling of the sheet, the edge positions of the sheet of recording medium at the edge sensor and at the head unit are not the same but are instead offset laterally.